What you are probably looking for is details on ERPNext custom scripts. There is not really a tutorial/guide to my knowledge, but I think the Cheatsheet is very helpful: Developer Cheatsheet · frappe/frappe Wiki · GitHub
The tutorial is designed to show the basic structure and interactions between Frappe infrastructure. You’ll be glad you did this afterwards, and just reading it isn’t usually enough, learn-by-doing is better in this case. </opinion
I was looking for something like that! I know something about JS and Python, but I don’t know how move through the inside of ERPNext.
Thank you very much!